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United States Government Accountability Office:
GAO:
Report to the Ranking Member, Committee on Science, Space, and
Technology, House of Representatives:
March 2011:
Energy-Water Nexus:
Amount of Energy Needed to Supply, Use, and Treat Water Is Location-
Specific and Can Be Reduced by Certain Technologies and Approaches:
GAO-11-225:
GAO Highlights:
Highlights of GAO-11-225, a report to the Ranking Member, Committee on
Science, Space, and Technology, House of Representatives.
Why GAO Did This Study:
Providing drinking water and wastewater services are two key functions
needed to support an urban lifestyle. To provide these services,
energy is needed to extract, use, and treat water and wastewater. As
the demand for water increases, the energy demands associated with
providing water services are similarly expected to grow.
GAO was asked to describe what is known about (1) the energy needed
for the urban water lifecycle and (2) technologies and approaches that
could lessen the energy needed for the lifecycle and barriers that
exist to their adoption. To address these issues, GAO reviewed
scientific studies, government-sponsored research, and other reports
and interviewed specialists from a variety of organizations, including
drinking water and wastewater utilities; federal, state, and local
government offices responsible for water or energy; and relevant
nonprofit groups, about the energy needed to move, use, and treat
water. GAO also selected three cities-—Memphis, Tennessee; San Diego,
California; and Washington, D.C.-—as illustrative case studies to help
understand the energy demands of the lifecycle in different areas of
the country.
GAO is not making any recommendations in this report. A draft was
provided to the Departments of Defense, Energy (DOE), and the
Interior, and the Environmental Protection Agency (EPA). DOE and EPA
provided technical comments, which we incorporated as appropriate.
What GAO Found:
Comprehensive data about the energy needed for each stage of the urban
water lifecycle are limited. In particular, few nationwide studies
have been conducted on the amount of energy used to provide drinking
water and wastewater services, and these studies do not consider all
stages of the lifecycle in their analysis. Specialists GAO spoke with
emphasized that the energy demands of the urban water lifecycle vary
by location. Considering location-specific and other key factors is
necessary to assess energy needs. The specialists mentioned such
factors as the topography of the area over which water is conveyed,
the level and type of treatment provided, and the quality of the
source water. For example, systems relying on groundwater as their
source for drinking water generally use less energy than systems
relying on surface water because groundwater usually contains fewer
contaminants and, therefore, requires less treatment before
distribution to customers.
A variety of technologies and approaches can improve the energy
efficiency of drinking water and wastewater processes, but barriers
exist to their adoption. Installing more efficient equipment, adopting
water conservation measures, and upgrading infrastructure are among
some of the approaches that can decrease energy use, according to
specialists GAO spoke with and studies GAO reviewed. For example,
technologies to identify potential pipeline leaks throughout water
systems can reduce water loss and the energy required to pump and
treat that “lost” water. However, according to specialists, adoption
of technologies and approaches to improve energy efficiency may be
hindered by the costs of retrofitting plants with more energy-
efficient equipment and competing priorities at treatment facilities,
among other barriers.
Figure: Key Stages of the Urban Water Lifecycle:
[Refer to PDF for image: illustration containing five photographs]
Drinking water processes:
1) Extraction of water from the source and conveyance to the treatment
plant.
2) Drinking water treatment.
3) Distribution from the drinking water treatment plant to customers.
Customer use:
4) Use by residential and commercial/industrial/institutional
customers.
5) Collection from customers and conveyance to the wastewater
treatment plant.
Wastewater processes:
6) Wastewater treatment.
7) Effluent discharge.
Sources: GAO analysis. Photos from left to right: GAO; US EPA Photo,
Eric Vance; Art Explosion; DC Water; and GAO.
[End of figure]
View [hyperlink, http://www.gao.gov/products/GAO-11-225] or key
components. For more information, contact Anu Mittal or Mark Gaffigan
at (202) 512-3841 or mittala@gao.gov or gaffiganm@gao.gov.
[End of section]
Contents:
Letter:
Background:
Comprehensive Data about the Energy Needed for the Urban Water
Lifecycle Are Limited, However Energy Needs Are Influenced by Location-
Specific Factors:
Certain Technologies and Approaches Can Reduce Energy Use, but
Barriers Could Impede Their Adoption:
Agency Comments:
Appendix I: Objectives, Scope, and Methodology:
Appendix II: GAO Contacts and Staff Acknowledgments:
Figures:
Figure 1: Key Stages of the Urban Water Lifecycle:
Figure 2: Typical Drinking Water Treatment Process:
Figure 3: Typical Wastewater Treatment Process:
Figure 4: Solar Panels at San Diego's Otay Water Treatment Plant:
Abbreviations:
DOE: U.S. Department of Energy:
EPA: U.S. Environmental Protection Agency:
EPRI: Electric Power Research Institute:
NPDES: National Pollutant Discharge Elimination System:
USGS: U.S. Geological Survey:
VFD: variable frequency drive:
[End of section]
United States Government Accountability Office:
Washington, DC 20548:
March 23, 2011:
The Honorable Eddie Bernice Johnson:
Ranking Member:
Committee on Science, Space, and Technology:
House of Representatives:
Dear Ms. Johnson:
According to the U.S. Census Bureau, in 2005, 83 percent of the U.S.
population lived in metropolitan areas, up 6 percent from 2000.
[Footnote 1] Two key resources necessary to support an urban lifestyle
are drinking water and the infrastructure necessary to treat
wastewater. The average American is estimated to use about 90 gallons
of water and produce 66 to 192 gallons of wastewater each day,
according to the U.S. Environmental Protection Agency (EPA). As the
demand for drinking water and wastewater treatment in urban areas
grows, it is expected that water utilities will have to increasingly
seek out alternative sources of water and treatment methods to
increase the water supply, especially in areas of water scarcity where
demand outpaces supply. However, treating and using these alternative
sources, such as seawater, come with a cost because, in addition to
other factors, they tend to be heavily energy dependent.
Providing drinking water and wastewater services to an urban
environment involves extracting, moving, and treating water--referred
to as the urban water lifecycle (see figure 1).[Footnote 2] Energy
plays a crucial role throughout this lifecycle in the following ways:
* Drinking water processes. Energy is needed to extract raw water from
the source--such as lakes, rivers, and underground aquifers--and
convey it to the drinking water treatment facility, treat the water to
certain drinking water standards established under the Safe Drinking
Water Act,[Footnote 3] and distribute the treated drinking water to
customers.
* Customer use. Energy is needed to circulate, pressurize, and heat
water for use inside households and businesses, and for outdoor water-
related uses by customers, such as watering lawns.
* Wastewater processes. Energy is needed to convey wastewater to
treatment facilities, treat the wastewater to levels required under
the Clean Water Act,[Footnote 4] and discharge the treated effluent
into a receiving body of water.
Figure 1: Key Stages of the Urban Water Lifecycle:
[Refer to PDF for image: illustration containing five photographs]
Drinking water processes:
1) Extraction of water from the source and conveyance to the treatment
plant.
2) Drinking water treatment.
3) Distribution from the drinking water treatment plant to customers.
Customer use:
4) Use by residential and commercial/industrial/institutional
customers.
5) Collection from customers and conveyance to the wastewater
treatment plant.
Wastewater processes:
6) Wastewater treatment.
7) Effluent discharge.
Sources: GAO analysis. Photos from left to right: GAO; US EPA Photo,
Eric Vance; Art Explosion; DC Water; and GAO.
[End of figure]
As urban populations increase and the demand for water grows, the
energy needed for the urban water lifecycle is also expected to grow.
In this context, you asked us to review the energy needs of providing
drinking water and wastewater treatment services to urban users.
Specifically, the objectives of this review were to describe what is
known about (1) the energy needed for each stage of the urban water
lifecycle and (2) technologies and approaches that could lessen the
energy needs of the urban water lifecycle, as well as any identified
barriers that exist to their adoption.
To address both of these objectives, we conducted a systematic review
of studies and other documents that examine the energy required to
extract, move, use, and treat water, including peer-reviewed
scientific and industry periodicals, government-sponsored research,
and reports from nongovernmental research organizations. We also
selected a nonprobability sample of three cities to examine in greater
depth and better understand regional and local differences related to
urban water lifecycles: Memphis, Tennessee; San Diego, California; and
Washington, D.C. We chose these cities as illustrative case studies
based on criteria such as type of water source; water availability;
type of wastewater system; unique characteristics, such as potential
to treat seawater to help meet drinking water demands; and economic
factors, such as energy costs. While the information derived from our
analysis of these cities cannot be generalized to all U.S. cities,
these examples provide valuable insights regarding the complexities of
assessing the energy needs for the urban water lifecycle. For each of
these case studies, we analyzed documentation from, and conducted
interviews with, a wide and diverse range of specialists from
organizations involved in all stages of the urban water lifecycle.
These organizations included drinking water and wastewater treatment
facilities, and state and local agencies responsible for water or
energy.[Footnote 5]
In addition to specialists associated with the illustrative case
studies, we interviewed a range of other knowledgeable individuals
whom we identified as having expertise related to the energy needs of
all stages of the urban water lifecycle throughout the United States.
We selected these specialists using an iterative process, soliciting
additional names from each person we interviewed. From among those
identified, we interviewed specialists who could provide us with a
broad range of perspectives on the energy needs of the urban water
lifecycle. We also interviewed specialists whom we identified during
our systematic review of studies who have analyzed (1) the energy
needed in one or more stages of the water lifecycle at the national or
local level or (2) techniques available to reduce the energy demands
for water. These specialists represented a variety of organizations,
including drinking water and wastewater treatment facilities; state
and local government offices responsible for water or energy;
officials from EPA and researchers from some of the U.S. Department of
Energy's (DOE) national laboratories, such as Sandia National
Laboratory; university researchers; water and energy industry
representatives from groups such as the American Water Works
Association and the Water Research Foundation; and relevant
nongovernmental organizations, such as the Pacific Institute, a
nonpartisan research institute that works to advance environmental
protection, economic development, and social equity. The specialists
also included individuals with knowledge of the energy demands for
water in other states, including Arizona, Colorado, Florida, New York,
and Wisconsin, to provide a better understanding of water and energy
issues in other regions around the United States.
We also interviewed other federal agency officials, scientists, and
researchers and analyzed data and information from federal agencies
that have responsibilities related to the energy needs of the urban
water lifecycle--the Department of Defense's U.S. Army Corps of
Engineers, DOE, the Department of the Interior's U.S. Geological
Survey (USGS) and Bureau of Reclamation, EPA, and the National Science
Foundation. We performed our work from January 2010 to January 2011 in
accordance with all sections of GAO's Quality Assurance Framework that
are relevant to our objectives. The framework requires that we plan
and perform the engagement to obtain sufficient and appropriate
evidence to meet our stated objectives and to discuss any limitations
in our work. We believe that the information and data obtained, and
the analysis conducted, provide a reasonable basis for any findings
and conclusions in this product.
Background:
According to EPA, about 52,000 community water systems use energy to
treat and deliver drinking water to over 290 million
Americans.[Footnote 6] In a typical drinking water treatment plant,
large debris and contaminants are physically removed from the raw
water using screens (see figure 2). Next, dirt and other particles
suspended in the water are removed through the addition of alum and
other chemicals during the processes of coagulation and sedimentation.
After these particles have separated out, the water passes through
filters made of layers of materials such as sand, gravel, and charcoal
to remove even smaller particles. At this point, the water is stored
in a closed tank or reservoir, allowing time for disinfection which
kills many disease-carrying organisms. The treated water is
pressurized for distribution to consumers. The distribution
infrastructure consists of pumps, pipes, tanks, valves, hydrants, and
meters that support delivery of water to the customer and control flow
and water pressure.
Figure 2: Typical Drinking Water Treatment Process:
[Refer to PDF for image: illustration]
Depicted in the illustration are the following process stages:
Water flow:
* Source water:
* Coagulation:
- Alum added:
- Other chemicals added:
* Sedimentation:
* Filtration:
- Sand:
- Gravel;
- Charcoal:
* Disinfection:
* Storage:
* Use.
Source: GAO analysis.
[End of figure]
Once water is delivered, residential consumers use it for a variety of
purposes, including for drinking; bathing; preparing food; washing
clothes and dishes; and flushing toilets, which can represent the
single largest use of water inside the home. Energy is needed to
accomplish many of these activities. For example, energy is used in
homes to filter and soften water and to heat it for use in certain
appliances, which accounts for 12.5 percent of a typical household's
energy use, according to DOE. In addition to residential water users,
commercial, industrial, and institutional customers use energy for
water-related purposes. For example, energy is used to produce hot
water and steam for heating buildings, to cool water for air
conditioning buildings, and to generate hot water needed to
manufacture or process materials, such as food and paper.
After water is used by customers, energy is needed to collect and
treat wastewater, and to discharge effluent into a water body.
Wastewater service is provided to more than 220 million Americans by
about 15,000 municipal wastewater treatment facilities.[Footnote 7]
During a typical wastewater treatment process, solid materials, such
as sand and grit, organic matter from sewage, and other pollutants,
are removed before the treated effluent is discharged to surface
waters. Systems for collecting, treating, and disposing of municipal
wastewater vary widely in terms of the equipment and processes used,
and wastewater may go through as many as three treatment stages--
primary, secondary, and advanced treatment--before water is discharged
(see figure 3).
* Preliminary and primary treatment. As wastewater enters a treatment
facility, it is screened to remove large debris and then passes
through a grit removal system to separate out smaller particulate
matter. After preliminary screening and settling, primary treatment
removes solids from the wastewater through sedimentation. Solids
removed during the treatment process may be further treated and used
for other applications, such as fertilizer; incinerated; or disposed
of in landfills.
* Secondary treatment. After primary treatment, the wastewater
undergoes secondary treatment to remove organic matter and suspended
solids through physical and biological treatment processes. Activated
sludge is the most commonly used biological treatment process in
secondary treatment of wastewater. This process relies on micro-
organisms to break down organic matter in the wastewater. More
specifically, aeration--whereby blowers or diffusers inject oxygen
into the wastewater--enables the micro-organisms to digest the organic
matter. After being pumped into an aeration tank to allow time for
digestion, the wastewater is next pumped to a secondary settling tank
for removal of digested material. After secondary settling, the
effluent either is disinfected and discharged into a water body, or it
undergoes advanced treatment.
* Advanced treatment. Most wastewater goes through at least secondary
treatment. However, before treated wastewater can be released in some
receiving waters, it may need to be further treated to reduce its
effect on water quality and aquatic life after discharge. Over 30
percent of wastewater treatment facilities provide this kind of
advanced treatment, which can remove additional contaminants.
Figure 3: Typical Wastewater Treatment Process:
[Refer to PDF for image: illustration]
Primary:
Wastewater:
Screening/grit removal;
Sedimentation:
Secondary:
Biological treatment processes such as activated sludge:
- Solids processing
- Disposal;
Secondary setting:
- Disinfection;
- Effluent discharge:
Advanced:
Removal of additional contaminants such as nutrients:
- Disinfection;
- Effluent discharge:
Source: GAO analysis.
[End of figure]
Two key pieces of federal legislation--the Safe Drinking Water Act and
the Clean Water Act--govern the treatment of drinking water and
wastewater. Each municipality or water utility generally may choose
amongst technologies for achieving a given standard. Under the Safe
Drinking Water Act, EPA has established National Primary Drinking
Water Standards for specified contaminants and has the authority to
regulate additional contaminants that the agency determines may have
adverse health effects, are likely to be present in public water
supplies, and for which regulation presents a meaningful opportunity
for health risk reduction. EPA's regulations establish a limit, or
maximum contaminant level, for specific contaminants and require water
systems to test the water periodically to determine if the quality is
acceptable.[Footnote 8] EPA has regulations in place for 89
contaminants, including disinfectants, byproducts of disinfectants,
and microbial contaminants, but has not issued a regulation under the
Safe Drinking Water Act for a new contaminant since 2000.
The Clean Water Act governs the discharge of pollutants into the
waters of the United States, including the treatment of wastewater
discharged from publicly owned treatment facilities. Specifically,
industrial and municipal wastewater treatment facilities must comply
with the National Pollutant Discharge Elimination System (NPDES)
permits that control pollutants that facilities may discharge into the
nation's surface waters. The act requires that municipal wastewater
treatment plants provide a minimum of secondary treatment prior to
discharge. In some cases, modification of secondary treatment
requirements may occur, however, for discharges into marine waters
under certain conditions. For example, the discharge may not interfere
with that water quality which assures protection of public water
supplies and the protection and propagation of a balanced, indigenous
population of shellfish, fish, and wildlife and allows recreational
activities on the water. In 2000, Congress amended the Clean Water Act
to require permits for discharges from combined sewers--sewers that
transport both wastewater and stormwater to the municipal wastewater
treatment plant--to conform with EPA's Combined Sewer Overflow Control
Policy, which requires systems to demonstrate implementation of
certain minimum pollution control practices.[Footnote 9] Combined
sewers may overflow when there is heavy precipitation or snowmelt,
resulting in the discharge of raw sewage and other pollutants into
receiving water bodies.
Comprehensive Data about the Energy Needed for the Urban Water
Lifecycle Are Limited, However Energy Needs Are Influenced by Location-
Specific Factors:
Comprehensive data about the energy needed for each stage of the urban
water lifecycle are limited, and few nationwide studies have been
conducted on the amount of energy used to provide drinking water and
wastewater treatment services to urban users. However, specialists
with whom we spoke emphasized that the energy demands of the urban
water lifecycle vary by location; therefore, consideration of location-
specific and other factors is key to assessing the energy needs of the
urban water lifecycle. These factors include the source and quality of
the water, the topography of the area over which water is conveyed and
the distance of conveyance, and the level and type of treatment
required.
Comprehensive Data on the Energy Needed to Support the Urban Water
Lifecycle Are Limited:
Providing a reliable and comprehensive estimate of the total energy
requirements for moving, treating, and using water in urban areas is
difficult, in part, because comprehensive data on the energy demands
of the urban water lifecycle are limited and few nationwide studies
have been conducted to quantify the amount of energy used throughout
the lifecycle. Two studies most often cited by the specialists we
spoke with were conducted by the Electric Power Research Institute
(EPRI) on the energy needs of the urban water lifecycle. These studies
concluded that 3 to 4 percent of the nation's electricity is used to
move and treat drinking water and wastewater. While some specialists
noted that these studies provide reasonable estimates of the energy
demands of the urban water lifecycle, other specialists raised a
number of concerns with the studies. In particular, according to
several specialists, the EPRI studies are outdated. The first study
dates back to 1996, and the more recent study was conducted in 2002
but relied on projections of future water use based on statistics
compiled in 2000. Some specialists also told us these studies do not
reflect the treatment processes that have been implemented over the
last decade, which have increased the amount of energy needed to treat
water. In addition, the studies do not include all stages of the urban
water lifecycle--specifically, they omit energy used by customers.
Because they exclude end use, the EPRI studies underestimate the
energy demands of the entire lifecycle because customer end use,
including use by residential customers, can be the most energy-
intensive stage of the entire lifecycle, according to some specialists
we spoke with and studies that we reviewed. Some specialists also
added that the studies underestimate total energy demands because they
include only electricity, excluding other fuel types that can be used
throughout the lifecycle. For example, the studies do not assess the
use of natural gas, which can be a primary energy source at wastewater
treatment plants for certain processes. Furthermore, some specialists
explained that the studies do not use actual measured data, relying
instead on previously published estimates of energy used for portions
of the water lifecycle.
Furthermore, some specialists noted that there are limited data on the
amount of energy associated with customer water use. Federal agencies
like DOE's Energy Information Administration collect some data on
energy used to heat water in residences and in the commercial sector,
but these data are reported on a national level and do not allow for
analysis at the local level. In addition, data needed to get a full
picture of the energy needs for water in an urban setting may not be
readily available at the local level. Specifically, water utilities
may not have detailed data on their facilities' energy use, may not
have conducted audits to understand how their facilities use energy,
or may be reluctant to share data, according to specialists we spoke
with.
Consideration of Location-Specific and Other Factors Is Key to
Assessing the Energy Needs of the Urban Water Lifecycle:
Many of the specialists told us that efforts to assess the energy
needs of the urban water lifecycle on a national scale can be
difficult, and the majority of the specialists we spoke with
emphasized that to obtain a more accurate picture, one needs to
consider location-specific and other factors that influence energy
use. The specialists identified the following as key factors that must
be considered for such an assessment.
Type of water source. Drinking water systems that rely on surface
water are often designed to take advantage of gravity and use little
to no energy to extract water from the source and convey it to the
treatment facility. In contrast, systems that rely on groundwater
require more energy for extraction because water must be pumped to the
surface from underground aquifers, especially if they rely on deep
underground aquifers. For example, Washington, D.C., which relies on
surface water, withdraws its water from two locations--Great Falls Dam
and Little Falls Dam--on the Potomac River. Most of the water is
withdrawn at Great Falls Dam and conveyed via gravity to the treatment
plant, using little energy during the extraction and conveyance
process. In contrast, extraction of water is an energy-intensive
process for Memphis, which relies on groundwater that is extracted
from over 160 wells that draw water from aquifers including the
Memphis Sand Aquifer, located 500 to 600 feet below ground.
Quality of water to be treated. The quality of water also impacts the
amount of energy needed for treatment, with higher-quality water
containing fewer contaminants and, therefore, requiring less treatment
than lower quality water. For example, treating groundwater generally
uses less energy than treating surface water because groundwater is
typically of higher quality than surface water. As a result, cities
that rely on groundwater as the source for their drinking water, such
as Memphis, generally use less energy for treatment than cities that
rely on surface water, such as Washington, D.C. However, the type of
contaminants in water can also affect the energy required for
treatment. For example, as one specialist noted, if groundwater
contains arsenic, treating this type of contamination can require the
use of more energy-intensive treatment technologies than treating
surface water that is extracted from a protected watershed or clean
snowmelt.
Topography and distance. Pumping water is one of the most energy-
intensive aspects of the urban water lifecycle, accounting for 80 to
90 percent of the energy used to supply drinking water in some
systems, and most of this energy is used to distribute water to
customers. The energy demand of pumping is affected by the topography
over which the water must be moved and the distance the water must
travel to treatment plants after extraction and to customers after
treatment.[Footnote 10] For example, San Diego gets a large amount of
its water from northern California. Transporting this imported water
to southern California is energy intensive because the water must be
conveyed hundreds of miles and lifted 2,000 feet over the Tehachapi
Mountains. Furthermore, because of the hilly terrain in some parts of
the city and the great expanse over which the customers are
distributed, additional energy is needed to pump water from the
treatment plants to consumers.
Condition of water system. The age of a system and the condition of
its pipes and equipment can also impact the energy demands of
providing drinking water and wastewater treatment services.
Specifically, older systems can be less energy efficient if the
equipment and infrastructure have not been properly maintained. The
American Society of Civil Engineers recently evaluated America's
drinking water and wastewater infrastructure and assigned both systems
a grade of a D-minus. The assessment noted that these systems contain
facilities that are nearing the end of their useful lives and need
upgrades to meet future regulatory requirements. In addition, the
condition of pipelines also has energy implications. According to some
specialists we spoke with, up to 50 percent of water is lost through
leaking pipes, which results in a loss of the energy that was used to
extract, convey, and treat the water. Furthermore, if pipelines are
not routinely cleaned, blockages can lead to friction in the pipes,
requiring additional energy to push water through these pipes.
Required treatment level. Energy needed for drinking water and
wastewater treatment is affected by the treatment levels required to
meet existing water quality standards, with each additional treatment
level increasing energy demands. In the case of wastewater treatment,
characteristics of the water body into which treated effluent is
discharged can impact the required level of treatment. For example,
San Diego officials told us the city's wastewater treatment facility
has been granted a modified permit by EPA. According to these
officials, this permit allows San Diego to treat its wastewater only
to an advanced primary level in part because years of ocean monitoring
have shown that the plant discharges have no negative impact to the
Pacific Ocean.[Footnote 11] If the city had to treat its wastewater to
secondary treatment levels, city officials estimate that its energy
usage would increase six to nine times as a result of having to use
more energy-intensive technologies to meet these higher standards.
Type of treatment process. The type of treatment process used at
drinking water and wastewater facilities also influences the energy
demands of providing drinking water and wastewater services to urban
users. For example, treatment plants that use the activated sludge
process for secondary treatment use more energy than plants that use
other processes, such as trickling filters or lagoon systems.[Footnote
12] The activated sludge process can account for 70 percent of a
wastewater treatment plant's energy consumption because of the energy
needed to power the blowers that pump oxygen into the wastewater to
sustain the micro-organisms. Furthermore, according to many of the
specialists we spoke with, a number of the new technologies used in
drinking water treatment plants are more energy intensive than
traditional treatment technologies. For example, some treatment plants
are installing ultraviolet light disinfection processes that are more
energy intensive, accounting for 10 to15 percent of a plant's total
energy use, than traditional disinfection with chlorine.[Footnote 13]
Other energy-intensive technologies that are increasing energy demands
for water treatment include filtration using membranes and ozonation,
a process that destroys bacteria and other micro-organisms through an
infusion of ozone.
Water use and type of customer. Characteristics related to customer
water use, such as how and where water is consumed, can also influence
the amount of energy needed to provide water and wastewater services
to urban users, according to specialists we spoke with. Large amounts
of household energy are consumed by heating water for showering,
dishwashing, and other uses. These uses would require more energy than
other household uses, such as flushing toilets. In addition, some
specialists told us that where the water is used influences the amount
of energy consumed. For example, water used in tall apartment
buildings or skyscrapers requires energy-intensive pumps to move the
water to the top floors. Furthermore, according to some specialists we
spoke with, the type of customer, such as whether the customer is
residential or industrial, affects the energy demands of providing
water and wastewater services. For example, Memphis has two wastewater
treatment plants, one of which is located in an industrial section of
the city and receives a higher percentage of its wastewater from
industrial sources than the other facility, which receives a higher
percentage of its wastewater from residential sources. Because the
industrial wastewater contains increased levels of organic
contaminants and thus requires more energy for treatment, the two
facilities consume different amounts of energy on a per-gallon basis.
Water availability. As current water supplies diminish, some cities,
especially those in areas that are already water stressed, are moving
toward alternative water supply sources that will require more energy
for treatment than processes used for surface water and groundwater.
For example, to help meet future demands for water and reduce
dependence on imported water supplies in San Diego, the region is
pursuing energy-intensive seawater desalination, which can be 5 to 10
times more energy intensive than conventional processes to treat
surface water and groundwater. Other areas, such as Tucson, Arizona,
that do not have ready access to seawater are pursuing desalination of
brackish groundwater--water that is less saline than seawater but that
contains higher saline levels than found in freshwater. Although
treating brackish water is less energy intensive than seawater
desalination, it still can use two to three times more energy than
conventional water treatment processes for freshwater supplies.
Furthermore, San Diego is studying the viability of treating a portion
of its reclaimed water--wastewater effluent that is treated to an
advanced level and suitable for nonpotable water applications such as
irrigation--for potable water use. To implement such a system, San
Diego would need to add energy-intensive advanced treatment processes
to its current wastewater treatment system. However, because this
additional energy use would offset the energy demands for imported
water, city officials told us the project is expected to result in a
net reduction in San Diego's energy profile. Using reclaimed water can
also increase energy demands for pumping, depending on the design of
the existing wastewater system. That is, many wastewater collection
systems were designed with treatment plants located in low elevation
areas to take advantage of gravity in conveying the wastewater to the
plant. However, if wastewater is recycled, energy could be needed to
pump this water against the flow of gravity into the distribution
system, but such increases may actually be less energy intensive than
reliance on imported water.
Future regulatory changes. To address growing concerns about emerging
contaminants and nutrients in the nation's water bodies, according to
many specialists, additional or more stringent regulatory standards
could increase the energy demands of treatment processes in the
future. Specifically, any more stringent standards that are
promulgated would most likely require additional levels of treatment,
and energy-intensive technologies, such as ozonation and membrane
filtration, may be necessary to meet such new standards. More
stringent regulations in the future could also increase energy demands
even for facilities that have already implemented such technologies.
For example, according to officials of the Washington, D.C.,
wastewater treatment plant, while the facility already must meet the
nation's most stringent permit requirements and uses advanced
treatment processes, stricter standards are expected to increase the
plant's energy demands, in part, because new energy-intensive
technologies may need to be added to the plant's treatment process.
Regulatory changes could also increase energy demands at other stages
of the urban water lifecycle. For example, higher standards for
effluent discharge from wastewater treatment plants could increase the
energy required for treatment. Furthermore, stricter water quality
standards for receiving waters could necessitate more plants to employ
advanced treatment standards, resulting in increased energy use for
the additional treatment or to pump effluent farther away to other
waters.
Complexity of water systems. In addition to location-specific factors,
the complexity of some urban water systems can make assessing the
energy demands of the urban water lifecycle challenging. For example,
some urban water systems like San Diego's are highly complex,
involving a number of different entities that have responsibility for
different parts of the system. Specifically, the City of San Diego
currently imports 85 to 90 percent of its water from the Colorado
River and northern California. In addition, the city's regional
drinking water, wastewater, and recycled water systems are managed by
a number of different organizations responsible for conveying drinking
water, wastewater, and recycled water to multiple treatment facilities
with over 160 pumping stations spread over 400 square miles within the
City of San Diego's service territory alone. As a result, collecting
consistent data on energy use from each of these organizations is
challenging, according to San Diego water officials we spoke with.
Certain Technologies and Approaches Can Reduce Energy Use, but
Barriers Could Impede Their Adoption:
Specialists we spoke with and studies we reviewed identified a variety
of technologies and approaches that can improve the energy efficiency
of drinking water and wastewater processes associated with the urban
water lifecycle, and determining the appropriate solution depends on
the circumstances of a particular system. However, adoption of these
technologies and approaches may be hindered by costs; inaccurate water
pricing; barriers associated with operational factors, such as limited
staffing levels at water utilities; competing priorities at drinking
water and wastewater facilities; and lack of public awareness about
the energy demands of the urban water lifecycle.
Certain Technologies and Approaches Can Reduce the Energy Use of the
Urban Water Lifecycle:
Several key technologies and approaches are currently available that
can improve the energy efficiency of drinking water and wastewater
processes, but determining the most appropriate solution depends on
the circumstances of a particular system and requires an understanding
of the system's current energy use. Many studies that we reviewed and
specialists we spoke with identified process optimization, equipment
and infrastructure upgrades, water conservation, and improved energy
management as approaches that can help reduce the energy demands for
water. In addition, the increased use of renewable energy could offset
the energy purchased by water utilities from energy providers.
Process Optimization:
According to some studies we reviewed, energy consumption by water and
wastewater utilities can comprise 30 to 50 percent or more of a
municipality's energy bill. Optimizing drinking water and wastewater
system processes, including energy-intensive operations like pumping
and aeration, was identified in many studies that we reviewed as an
approach to reducing the energy demands of the urban water lifecycle.
Implementing monitoring and control systems and modifying pumping and
aeration operations are some ways to reduce energy use through process
optimization.
* Implementing monitoring and control systems. Monitoring and control
systems, also known as supervisory control and data acquisition
systems, can be used to optimize drinking water and wastewater
operations. Such systems provide a central location for monitoring and
controlling energy-consuming devices and equipment, which provides
plant operators with the ability to schedule operations or
automatically start and stop devices and equipment to manage energy
consumption more effectively and improve overall operations.
* Modifying pumping operations. A variety of modifications could
increase the efficiency of pumping systems. For example, operating
constant speed pumps as near as possible to their most efficient
speed, using higher efficiency pumps as opposed to lower efficiency
pumps, and operating multiple smaller pumps rather than a few large
pumps to better match pumping needs can help maximize pumping
efficiency. In addition, using devices to monitor and control pump
speeds--known as variable frequency drives (VFD)--may allow facility
operators to accommodate variations in water flows by running pumps at
lower speeds and drawing less energy when water flows are low.
Potential energy savings from the use of VFDs can range from 5 to 50
percent or more, according to studies we reviewed. However, these
studies and some specialists we spoke with also noted that VFDs are
not necessarily well suited for all applications--such as when flow is
relatively constant--and that potential benefits of VFDs should be
evaluated based on system characteristics, such as pump size and
variability of flow.
* Modifying aeration operations. According to many studies we reviewed
and specialists we spoke with, aeration in wastewater treatment
consumes a significant amount of energy, and systems can be
reconfigured and better controlled to improve energy efficiency.
Specifically, blowers and mechanical aerators are typically powered by
a large motor, and installing variable controls on blowers to enable
operators to better match aeration with oxygen requirements can reduce
energy demands. Likewise several studies noted that dissolved oxygen
control systems can be used to match oxygen supply with demand by
monitoring the concentration of dissolved oxygen in the wastewater and
adjusting the blower system or mechanical aerator speed accordingly.
In addition, probes can be installed to monitor dissolved oxygen
levels within the wastewater and signal operators when the system may
need adjustment.
Equipment and Infrastructure Improvements:
According to many studies and specialists we spoke with, installing
more efficient equipment--motors, pumps, blowers, and diffusers--for
energy-intensive processes such as aeration and pumping can reduce
energy use. In addition, ensuring the proper sizing and maintenance of
equipment and infrastructure can improve energy efficiency.
* Upgrading equipment. Replacing less efficient equipment with more
energy-efficient equipment can reduce energy use. For example,
installing more efficient motors could reduce energy use by 5 to 30
percent, according to studies we reviewed. In addition, blower and
diffuser technologies, including high-speed "turbo" blowers and fine
or ultra-fine bubble diffusers, could decrease the energy demands of
aeration. High-speed turbo blowers use less energy than other blower
types, although, because these blowers are a new technology and
relatively few are in use, efficiency claims are not yet well
documented, according to a 2010 EPA report.[Footnote 14] Energy-saving
estimates for fine bubble diffusers, which have higher oxygen transfer
efficiencies than coarse bubble diffusers, range from 9 to 50 percent
or more, but some specialists and studies expressed concerns about
maintenance requirements as well as the durability of this technology.
* Right-sizing equipment. Many wastewater treatment systems were
designed to handle greater capacity in the future because of
anticipated population growth. However, this growth has not always
occurred and, as a result, existing equipment may be oversized and
consume more energy than is needed to treat current flows, according
to some specialists we spoke with. Proper sizing and selection of
pumping and aeration equipment to more closely match system needs can
help maximize efficiency. For example, in Washington, D.C., the
operators of the wastewater treatment plant replaced a 75-horsepower
motor with a 10-horsepower motor in one facility to better meet actual
energy demands.
* Improving maintenance and leak detection technology. Periodic
inspections to assess pump performance and the need for replacement or
maintenance of electrical systems and motors can increase the energy
efficiency of the overall system, according to studies we reviewed. In
addition, leak detection technologies can identify leaks throughout
water systems, thereby reducing water loss and the related energy
required to pump and treat that "lost" water. For example, acoustic
leak detection systems use sensors to monitor for sounds that may
indicate potential leaks and relay the data back to a central control
room, which helps water utility staff identify actual leaks and
schedule maintenance accordingly. The San Diego County Water
Authority, which provides water to San Diego and other areas in
southern California, has fiber optic lines in place to monitor its
pipeline 24 hours a day to detect evidence of leaks.
Water Conservation and Efficiency:
Many studies we reviewed and specialists we spoke with also identified
water conservation as an approach to reducing the energy needed for
the urban water lifecycle. Several studies noted that decreased
customer water use could directly translate into energy savings.
Furthermore, water conservation also reduces the amount of energy used
to convey, treat, and distribute drinking water to the customers.
Studies we reviewed and specialists we spoke with identified a variety
of tools that utilities can use to promote water conservation,
including enhanced metering, increased water prices, public education,
and incentives to install water-efficient appliances. For example, San
Diego is implementing advanced metering tools to better manage its
system and to provide real-time information to customers regarding
their water use in order to help them make choices that conserve
water. In addition, EPA has developed water efficiency and performance
criteria for several product and program categories through
WaterSense, a federal water efficiency program.[Footnote 15]
Energy Management:
While many technologies and approaches have been identified to reduce
the energy demands for water, determining the most appropriate
solution depends on the circumstances of a particular system--
including the type of facilities and treatment processes in place--and
requires an understanding of current energy use. Several studies we
reviewed identified improved energy management, including conducting
energy audits of treatment facilities or systems, as a necessary first
step to reducing energy demands. Specifically, specialists told us
that by providing utility managers with information about their
facilities' energy use, energy audits can help managers identify
opportunities to change plant operations in ways that will save
energy. For example, the energy supplier for one wastewater treatment
plant in Memphis conducted an energy audit of the blower system, which
used about 75 percent of the plant's total energy. As a result of this
audit, operators changed their practices to run blowers at the lowest
levels possible while still ensuring they continued to meet the
effluent discharge standards required by the plant's permits.
Similarly, in 2000, San Diego established an in-house energy
management program, which includes an audit team that looks for
technologies and approaches to lessen the energy demands of the city's
drinking water and wastewater systems. The team studies the efficiency
of existing equipment and treatment processes and considers upgrading
or replacing equipment with available energy-efficient technologies.
For example, the energy audit team identified over a dozen energy
conservation measures that could be applied to reduce energy
consumption at two of the city's sewer pump stations, including
installing timers to turn off lighting and upgrading, resizing, and
replacing motors and blowers.
In addition, EPA's Energy Star program provides energy management
tools and strategies to support the successful implementation of
energy management programs. Officials told us that EPA also works with
municipal drinking water and wastewater utilities to provide
information on potential energy efficiency opportunities. EPA's online
benchmarking tool, known as the Portfolio Manager, offers wastewater
treatment plant managers the opportunity to compare the energy use of
their plants with that of other plants using the EPA energy
performance rating system. EPA has also published a variety of
educational materials for drinking water and wastewater utilities to
help identify, implement, measure, and improve energy efficiency and
renewable energy opportunities.
Other Approaches:
Specialists we spoke with and studies we reviewed identified two
additional approaches for reducing the energy required to treat and
distribute water: improving advanced treatment technologies and
redesigning a city or region's water system.
* Improving advanced treatment technologies. According to EPA
officials, and as previously noted by specialists, improving energy-
intensive advanced treatment technologies--such as ultraviolet
disinfection, ozone, and membrane technologies--is important because
plants are increasingly using them. For example, the use of membrane
materials that require less pressure to push water through to remove
contaminants could decrease the energy demands of that technology. In
addition, some specialists we spoke with told us that newer
technologies are being developed, such as forward osmosis, that may
offer alternative treatment approaches that are more efficient than
the technologies currently used for desalination. Several specialists
told us the federal government should conduct additional research to
understand and improve the energy efficiency of water supply,
treatment, and water use--for example, by conducting more research on
energy-efficient desalination technologies.
* Redesigning water systems. Some specialists noted that redesigning
water systems in ways that better integrate drinking water,
wastewater, and stormwater management could improve the energy
efficiency of water systems overall. Decentralizing treatment systems,
implementing approaches to better manage stormwater, reusing
wastewater, and using less energy-intensive processes for biological
treatment can help reduce energy needed for providing drinking water
and wastewater services. For example, current water systems primarily
rely on a few plants with large capacities to treat drinking water and
wastewater. Some specialists told us that systems could be redesigned
to incorporate more treatment plants with smaller capacities and to
locate these plants closer to the point of water use by customers,
thereby reducing some of the energy required for pumping to the
treatment site. In addition, some specialists identified improvements
in stormwater management through strategies such as low-impact
development--which involve land use planning and design to better
manage stormwater--as a way to reduce the energy required for
treatment. For example, by decreasing stormwater infiltration into
some wastewater systems through low-impact development activities such
as the capture and use of rainwater, flows into treatment plants would
also be reduced, thereby decreasing the energy needed for treatment.
In addition, reusing wastewater for purposes that may not require
potable water, such as industrial processes or landscaping, may reduce
overall energy use by decreasing energy used currently to pump, treat,
and distribute potable water to these customers, according to some
studies we reviewed. However, the potential for energy savings from
reuse depends on the energy intensity of a given system's water supply
as well as the level of treatment needed for potential uses.
Furthermore, some studies we reviewed and specialists we spoke with
noted that relying more on biological treatment processes that do not
require aeration, such as using lagoons or trickling filters, may be
an option to reduce energy demands. However, these approaches may be
limited by available space in urban areas and therefore may not be
applicable everywhere.
Renewable Energy:
Many studies we reviewed and specialists we spoke with stated that
drinking water and wastewater utilities could adopt renewable energy
projects to reduce energy purchased from energy providers. Renewable
energy projects may include solar, wind, and hydroelectric power as
well as the recovery and use of biogas from wastewater treatment
processes.[Footnote 16] In addition, some studies we reviewed and
specialists we spoke with identified hydro turbines as an option for
recovering energy in the distribution system. For example, water
systems with changes in topography that have pressure-reducing valves
in place can install turbines that generate electricity as water flows
past. This energy could then be recovered for use in powering
equipment.
The city of San Diego has adopted a variety of renewable energy
projects to power its drinking water and wastewater treatment
operations. For example, the city installed a 945-kilowatt solar power
system at the Otay Water Treatment Plant that produces enough
electricity to meet the power needs of the plant's pumping operation
(see figure 4). In addition, at the city's Point Loma Wastewater
Treatment Plant, both methane and hydroelectric power are recovered
from wastewater processes. The plant uses digestion processes to treat
organic solids resulting from its wastewater treatment processes.
Methane, a by-product of the digestion process, is removed from the
digesters and used to power two engines that supply all of the plant's
energy needs, making it energy self-sufficient. In addition, the plant
recovers hydroelectric power from the treated effluent that it
discharges into the ocean. The effluent drops 90 feet from the
wastewater treatment plant to the ocean, powering a 1,350 kilowatt
hydroelectric plant. The city can sell any excess energy produced by
the plant back to the electric utility.
Figure 4: Solar Panels at San Diego's Otay Water Treatment Plant:
[Refer to PDF for image: photograph]
Source: San Diego Public Utilities Department.
[End of figure]
While renewable energy projects have the primary benefit of reducing
the energy needed by water treatment facilities from outside
providers, such projects could also reduce overall energy use. For
example, solar power systems co-located at treatment facilities in San
Diego may result in the offset of slightly more electricity than they
produce, since electricity generated by the energy provider off-site
and transferred over a greater distance results in some loss of energy
during transmission.
Key Barriers Could Impede Adoption of Technologies and Approaches:
Specialists we spoke with identified a number of key barriers to
adopting the available technologies and approaches that could reduce
the energy demands of the urban water lifecycle. These barriers fall
into five categories: (1) costs associated with these technologies,
(2) inaccurate water pricing, (3) barriers associated with how water
utilities operate, (4) competing priorities at drinking water and
wastewater facilities, and (5) the lack of public awareness about the
energy demands of the urban water lifecycle.
Costs Associated with Energy-Saving Improvements:
Energy-saving technologies may lessen the energy demands of the urban
water lifecycle, but such improvements are often expensive to adopt.
Many specialists told us that, as a result, utilities may not be able
to justify the costs necessary to install energy-efficient equipment.
For example, some specialists told us that upgrading to VFDs, higher-
efficiency pumps, and ultra-fine bubble diffusers may lessen a water
facility's energy demands, but the costs of installing these
technologies can be prohibitive for some systems, and it can take
years to realize the full energy-saving benefits. As a result, some
utility operators may choose to wait until there is an immediate need
to upgrade equipment because the costs can be justified more easily at
that point. Similarly, some specialists told us that the cost of
installing renewable energy projects, such as solar panels, can be a
barrier to adoption for some treatment facilities. According to an
energy specialist we spoke with, it may take over 30 years to fully
realize the cost savings from such projects. However, a DOE official
noted that while expensive in the past, the cost of solar panels has
been decreasing in recent years. Furthermore, installing energy-
efficient equipment and infrastructure upgrades, such as replacing
leaking pipelines, can be particularly challenging for smaller water
utilities because they often compete for limited funds against other
municipal services, such as fire and police protection. In addition,
in areas where energy costs are low, there may be little incentive for
water utility operators to implement capital-intensive practices to
save energy. To help overcome the barriers associated with the costs
of upgrading facilities, some specialists told us that utilities
should conduct cost analyses to account for the total savings incurred
over the life of the energy-saving projects, not just focus on the
short-term returns on investment. Some specialists we spoke with also
suggested that utilities should take advantage of the federal funding
available through the Drinking Water and Clean Water State Revolving
Fund programs, which can be used to fund a variety of projects that
improve water and energy efficiency. These programs provide financial
assistance for drinking water and wastewater infrastructure projects,
respectively, and for certain other purposes, such as installing water
meters, installing or retrofitting water-efficient devices, and
promoting water conservation. In addition, the American Reinvestment
and Recovery Act of 2009 and EPA's fiscal year 2010 appropriation
encourage states to use a portion of those funds for such energy and
water efficiency projects.[Footnote 17]
Inaccurate Water Pricing:
According to many specialists with whom we spoke, the true cost of
water is often not reflected in rates customers are charged.
Specifically, specialists told us that water subsidies have kept water
rates artificially low and do not reflect the actual cost, including
energy costs, of pumping, treating, and moving drinking water and
wastewater. The effect of this situation is two-fold. First, there may
be little incentive for customers to use water more efficiently if
they are not paying the true cost of it. Second, because these reduced
water rates generally do not cover the actual costs incurred by
drinking water and wastewater facilities, some utilities do not
generate enough revenue to implement upgrades that could lessen their
facilities' energy demands. Some specialists noted, however, that rate
increases are not a politically popular approach and may be met with
public and political resistance.
Operational Challenges:
Other barriers to adopting energy-reducing technologies and approaches
are operational in nature. Specifically, specialists we spoke with
noted a number of such challenges, including utilities not having
staff with adequate knowledge about technologies and access to energy-
use data, reluctance to change, and lack of coordination between water
and energy utilities. For example, several specialists told us that
smaller utilities lack staff with knowledge about the energy-efficient
techniques or may only have operators in place part time to manage or
oversee new technologies. Because operators generally are the
advocates for energy-efficiency upgrades, the specialists believe it
could be difficult to gain support for such investments without
knowledgeable operators. Further, operators may be unaware of the
amount of energy their facilities use because, in many municipalities,
these bills are received and paid by other departments and operators
may not have access to these data. Consequently, operators may be
unaware of the potential for energy savings from upgrades. Moreover,
many specialists told us that operators are often resistant to alter
the practices that they have employed for years to move and treat
water and may be reluctant to adopt new technologies or approaches,
especially if the effectiveness of such changes has not yet been
adequately proven. Some specialists also told us that drinking water
and wastewater utilities do not coordinate as closely as they could
with energy utilities to identify opportunities to optimize their
operations and, thereby, lessen their energy demands.
Energy Usage Considerations Are Secondary to Complying with Water
Quality Regulations:
Considering the energy demands of treatment can be an afterthought to
complying with water quality regulations for treatment plant
operators, according to some specialists with whom we spoke. One
drinking water utility operator told us that energy is considered to
the extent possible when decisions are being made about altering
treatment processes to meet regulatory requirements but that the
safety of the water supply is his primary concern. For example, when
the city of San Diego's Public Utilities Department was considering
which disinfection technology to employ, it chose to use ozonation
because it would provide more effective disinfection for the plant and
also reduces disinfection by-products, even though it is a more energy-
intensive technology than the current disinfection process. In
addition, to ensure that minimum effluent discharge standards are met,
water utility operators may over-treat wastewater by, for example,
running aeration blowers at higher levels than necessary to meet
regulatory requirements. In light of the potential for more stringent
standards in the future, some specialists noted that regulators should
consider the energy demands associated with these increased water
quality standards.
Lack of Public Awareness about the Energy Demands of the Urban Water
Lifecycle:
Many specialists told us that many customers are not aware of and do
not understand the energy demands of drinking water and wastewater
services. While some customers may be aware of their total energy use,
it may not be clear to them how much of that energy use is for heating
water and other water-related uses. In addition, customers may not be
aware that water conservation saves not only water but also energy.
Some specialists told us that federal programs such as EPA's
WaterSense and Energy Star and some state efforts, such as in
California and New York, have begun to educate the public on the
energy demands of the urban water lifecycle; however, additional
efforts may be needed to increase awareness of the energy-water nexus
for providing drinking water and wastewater to urban users.
Agency Comments:
We provided a draft of this report to the Departments of Defense,
Energy, and the Interior and EPA for review and comment. DOE and EPA
provided technical comments that we incorporated into the final report
as appropriate.
As agreed with your office, unless you publicly announce the contents
of this report earlier, we plan no further distribution until 30 days
from the report date. At that time, we will send copies of this report
to the appropriate congressional committees; the Administrator of EPA;
the Secretaries of Defense, Energy, and the Interior; and other
interested parties. In addition, the report will be available at no
charge on the GAO Web site at [hyperlink, http://www.gao.gov].
If you or your staff have questions about this report, please contact
us at (202) 512-3841 or mittala@gao.gov or gaffiganm@gao.gov. Contact
points for our Offices of Congressional Relations and Public Affairs
may be found on the last page of this report. GAO staff who made key
contributions to this report are listed in appendix II.
Sincerely yours,
Signed by:
Anu K. Mittal:
Director, Natural Resources and Environment:
Signed by:
Mark E. Gaffigan:
Managing Director, Natural Resources and Environment:
[End of section]
Appendix I: Objectives, Scope, and Methodology:
Our objectives for this review were to describe what is known about
(1) the energy needed for each stage of the urban water lifecycle, and
(2) technologies and approaches that could lessen the energy needed
for the urban water lifecycle, as well as any identified barriers that
exist to their adoption. We focused our work on community drinking
water systems and publicly owned wastewater facilities located in the
United States. We also focused on residential customers and, to the
extent possible, commercial, industrial, and institutional customers.
To address both of these objectives, we conducted a systematic review
of studies and other documents that examine the energy required to
extract, move, use, and treat water, including peer-reviewed
scientific and industry periodicals, government-sponsored research,
and reports from nongovernmental research organizations. In conducting
this review, we searched databases such as ProQuest, EconLit, and
BioDigest, and used an iterative process to identify additional
studies, asking specialists to identify relevant studies and reviewing
studies from article bibliographies. We reviewed studies that fit the
following criteria for selection: (1) the research was of sufficient
breadth and depth to provide observations or conclusions directly
related to our objectives; (2) the research demonstrated the energy
demands of water supply systems in the United States; (3) the studies
typically were published between 2000 and 2010; and (4) the studies
were determined to be methodologically sufficient. We examined key
assumptions, methods, and relevant findings within the studies related
to drinking water processes, customer end use, and wastewater
processes. We believe we have included the key studies and have
qualified our findings, where appropriate. However, it is possible
that we may not have identified all of the studies with findings
relevant to these two objectives.
We also selected a nonprobability sample of three cities to examine in
greater depth to better understand regional and local differences
related to urban water lifecycles: Memphis, Tennessee; San Diego,
California; and Washington, D.C. We chose these cities as illustrative
case studies based on criteria such as their type of water source;
water availability; type of wastewater system; unique characteristics,
such as potential for desalination; and economic factors, such as
energy costs. The results from our visits to these cities cannot be
generalized to all U.S. cities, but they provide valuable insights as
illustrative case studies. For each of these case studies, we analyzed
documentation from and conducted interviews with a wide range of
specialists to gain the views of diverse organizations covering all
stages of the urban water lifecycle. These groups included relevant
drinking water and wastewater treatment facilities, and state and
local agencies responsible for water or energy. We requested
interviews with representatives from electrical utilities in each
location. In San Diego and Washington, D.C., the utilities did not
meet with us or told us they did not have relevant data. In Memphis,
however, which has a combined water and energy utility, an energy
official was present at our meeting with the utility, but the utility
told us it does not track data on energy for water-related uses for
some customer types. In addition, we conducted site visits to drinking
water and wastewater treatment facilities in each of these locations
to better understand the role that energy plays in their operation.
In addition to the specialists we interviewed as part of our
illustrative case studies, we also interviewed a range of specialists
whom we identified as having expertise related to the energy needs of
all stages of the urban water lifecycle in general. We selected these
specialists using an iterative process, soliciting additional names
from each person we interviewed. From among those specialists
identified, we interviewed those who could provide us with a broad
range of perspectives on the energy needs of the urban water
lifecycle. We also interviewed specialists that we identified during
our systematic review of studies who have analyzed (1) the energy
needed in one or more stages of the water lifecycle at the national or
local level or (2) techniques available to reduce the energy demands
for water. These specialists represented a variety of organizations,
including drinking water and wastewater treatment facilities; state
and local government offices responsible for water or energy;
officials from the EPA; researchers from some of the Department of
Energy's national laboratories, such as Sandia National Laboratory;
university researchers; water and energy industry representatives from
groups such as the American Water Works Association and the Water
Research Foundation; and relevant nongovernmental organizations, such
as the Pacific Institute, a nonpartisan research institute that works
to advance environmental protection, economic development, and social
equity. The specialists also included individuals with knowledge of
the energy demands for water in other states, including Arizona,
Colorado, Florida, New York, and Wisconsin, to gain a better
understanding of water and energy issues in other regions around the
United States. We also interviewed other federal agency officials and
analyzed data and information from federal agencies that have
responsibilities related to the energy needs of the urban water
lifecycle--the Department of Defense's U.S. Army Corps of Engineers,
the Department of Energy, the Department of the Interior's U.S.
Geological Survey and Bureau of Reclamation, the Environmental
Protection Agency, and the National Science Foundation.
To analyze information gathered through the interviews with
specialists and the scientific studies, research, and other key
documents reviewed, we conducted content analyses. Specifically, to
conduct the content analysis of information gathered through
interviews with specialists, we reviewed each interview, selected
relevant statements, and identified and labeled these statements using
a coding system that identified the topic area. Once relevant
statements from the interviews were extracted and coded, we used the
coded data to develop key themes. An independent reviewer then
verified that the codes were accurately applied to the statements and
the key themes were correctly developed. During the course of our
review, we conducted over 60 interviews with over 100 specialists. For
the purposes of our interview analysis, each interview represents the
views of one specialist even if more than one specialist was present
at the interview. We used the following categories to quantify
responses of experts and officials: "some" refers to responses from 2
to 5 specialists, "several" refers to responses from 6 to 10
specialists, and "many" refers to responses from 11 or more
specialists. We used a similar coding scheme to identify key themes
resulting from our analysis of the scientific studies, research, and
other key relevant documentation.
We performed our work from January 2010 to January 2011 in accordance
with all sections of GAO's Quality Assurance Framework that are
relevant to our objectives. The framework requires that we plan and
perform the engagement to obtain sufficient and appropriate evidence
to meet our stated objectives and to discuss any limitations in our
work. We believe that the information and data obtained, and the
analysis conducted, provide a reasonable basis for any findings and
conclusions in this product.
[End of section]
Appendix II: GAO Contacts and Staff Acknowledgments:
GAO Contacts:
Anu Mittal, (202) 512-3841 or mittala@gao.gov:
Mark Gaffigan, (202) 512-3841 or gaffiganm@gao.gov:
Staff Acknowledgments:
In addition to the contact named above, Elizabeth Erdmann, Assistant
Director; Colleen Candrl; Antoinette Capaccio; Janice Ceperich; Nancy
Crothers; Abbie David; Angela Leventis; Katherine Raheb; Ellery Scott;
Rebecca Shea; Jena Sinkfield; Kevin Tarmann; and Lisa Vojta made
significant contributions to this report.
[End of section]
Footnotes:
[1] A metropolitan area, as defined by the Office of Management and
Budget, consists of one or more counties containing at least one
urbanized area of 50,000 or more people.
[2] For the purposes of this report, "urban" refers to areas of the
country that are connected to community water systems and that receive
wastewater services from municipal wastewater treatment facilities. It
does not include agricultural water use or customers who self-supply
water or rely on septic systems for waste disposal.
[3] 42 U.S.C. §§ 300f-300j-26 (2006).
[4] 33 U.S.C. §§ 1251-1387 (2006).
[5] We requested interviews with representatives from the primary
electrical utilities in each location. In San Diego and Washington,
D.C., the utilities did not provide representatives to meet with us or
told us they did not have relevant data. In Memphis, however, which
has a combined water and energy utility, an energy official was
present at our meeting with the utility, but the utility told us it
does not track data on energy for water-related uses for some customer
types.
[6] A community water system is one that provides water for human
consumption through pipes or other constructed conveyances to at least
15 service connections, or regularly serves at least 25 people year-
round. Customers not part of a community water system can receive
water from other types of public water systems or from private wells.
[7] Wastewater may be treated through other systems, such as septic
systems, which serve approximately 25 percent of U.S. households.
[8] EPA may promulgate a treatment technique in lieu of a maximum
contaminant level, if the EPA Administrator makes a finding that it is
not economically or technologically feasible to ascertain the level of
a given contaminant in drinking water.
[9] 33 U.S.C. §1342(q) (2006) (implementing the Combined Sewer
Overflow Control Policy signed by the Administrator on April 11, 1994;
see 59 Fed. Reg. 18688 (Apr. 19, 1994)). The policy defines a combined
sewer system as a wastewater collection system owned by a state or
municipality that conveys sanitary wastewaters and stormwater through
a single-pipe system to a publicly owned treatment works treatment
plant.
[10] According to some specialists we spoke with, topography and
distance can also affect the energy needed to pump and move
wastewaster. However, the specialists noted that wastewater systems
were often designed to rely on gravity, and wastewater treatment
plants were located close to the receiving waters.
[11] Advanced primary treatment includes enhanced removal of solids
and organic matter from wastewater, which is typically accomplished by
chemical addition or filtration.
[12] A trickling filter is a bed of media, typically rocks or plastic,
through which the wastewater passes. A lagoon system uses a
scientifically constructed pond that allows sunlight, algae, bacteria,
and oxygen to interact and treat the wastewater.
[13] Treatment plants may also install ultraviolet light disinfection
technologies for reasons unrelated to water quality, such as concerns
about plant safety and security when storing large quantities of
chemicals on-site.
[14] Environmental Protection Agency, Evaluation of Energy
Conservation Measures for Wastewater Treatment Facilities (Washington,
D.C., 2010).
[15] WaterSense is an EPA-sponsored partnership program that seeks to
protect the future of our nation's water supply by promoting water
efficiency and enhancing the market for water-efficient products,
programs, and practices.
[16] Biogas is a mixture of gases including methane and carbon dioxide
produced during the digestion of organic solids that result from the
wastewater treatment process.
[17] American Recovery and Reinvestment Act of 2009, Pub. L. No. 111-
5, 123 Stat. 115, 169; Interior Department and Further Continuing
Appropriations, Fiscal Year 2010, 123 Stat. 2904, 2935.
[End of section]
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